1. Field of the Invention
The present invention relates generally to infrared thermometers. More specifically, it relates to the probe cover portion of an infrared thermometer, commonly known as tympanic or ear thermometer.
2. Description of Prior Art
Temperature of an object, specifically, of a human or animal, can be measured by the means of thermal conduction or, alternatively, by means of thermal radiation. In the latter case, naturally emanated electromagnetic radiation in the far infrared spectral range is detected by an appropriate sensor, whose output signal is indicative of the surface temperature of an object. A combination of a sensor, electronic circuit and other components form an infrared (IR) thermometer, which is an opto-electronic instrument.
Human or animal body temperature can be measured by placing an optical probe of an IR thermometer into the ear canal, because the tympanic membrane temperature is a recognized indicator of the core body temperature.
Nearly all medical contact thermometers, for example, oral or rectal, use sanitary probe covers. In a contact probe cover, thermal energy (heat) is transmitted by means of thermal conduction, thus, requirements to a probe cover shall comply with the thermally conductive properties of the probe cover material. Various conventional covers for such contact thermometers are described in many patents, for example, in U.S. Pat. No. 4,159,766 issued to Kluge.
For measuring surface temperature of an object without a physical contact, the IR probe is aimed at the area of interest. In medical applications, to measure temperature of a tympanic membrane and the surrounding tissues, the probe is placed into the ear canal. Before the insertion, a probe cover is installed onto the probe to envelop its parts that otherwise might come in contact with the object tissues. Such a cover shall not only provide a sanitary protection against contamination of the probe by ear wax and other soiling biological compounds, but also it shall possess other properties which are critical for accurate temperature measurement by means of detecting infrared signal. Such properties include a good transparency of the front portion of the probe cover in the spectral range of interest, low directional distortion of optical rays, tight manufacturing tolerances, stability of the optical properties during installation onto the probe, long term stability, etc. Probe covers for IR thermometers are exemplified U.S. Pat. No. 5,088,834 issued to Howe and Brown and U.S. Pat. No. 5,163,418 issued to Fraden et al. A probe cover for an IR thermometer differs significantly from a probe cover used with a conventional contact thermometer.
As a rule, any prior art probe cover intended for an IR thermometer employed a thin polymer membrane at its optical end (thickness ranging from as little as 0.0005 to as much as 0.005xe2x80x3). The IR radiation has to pass through that membrane before entering the probe and being detected by the IR sensor. In effect, such a probe cover works as an optical filter. Typical materials for fabricating the probe covers are polyethylene, polypropylene, and copolymers of the above.
When the probe cover is installed onto the IR thermometer probe and subsequently inserted into a body cavity (such as an ear canal), it is important to assure that optical properties of the membrane either remain unchanged, or change in a known and predictable fashion. Otherwise, the optical transmission of the cover may be altered which would result in an unacceptable magnitude of error in temperature measurement.
U.S. Pat. Nos. 4,662,360, 5,293,862 and 5,179,936 issued to O""Hara et al describe a tubular body of the probe cover with a bonded membrane where the tubular body may be injection molded. The tubular body is made of a pliant plastic material having thickness on the order of 0.010xe2x80x3. When installed on the IR thermometer probe, the membrane is stretched to smooth out the wrinkles. While removing the wrinkles may be beneficial, the stretching is undesirable as it cannot be well controlled due to manufacturing tolerances of the cover and the probe. This may result in variations in the front membrane transmission and, subsequently, in error.
The above indicated U.S. Pat. No. ""936 also describes a binding ring which supports a membrane and the ring is a part of the rigid tubular body of the probe cover (referred to in the patent as xe2x80x9cspeculumxe2x80x9d), yet the binding ring doesn""t prevent the film from stretching.
To prevent reuse of a probe cover, Twentier in U.S. Pat. No. 3,878,836 teaches a probe cover (xe2x80x9cspeculumxe2x80x9d) having a stretchable portion near the tip which cracks during the installation, thus it cannot be reused.
Summarizing prior art, two types of probe covers for the IR thermometers are: covers which are pre-shaped during the manufacturing process and those whose shape changes during the installation onto the probe. Both types have their own advantages and disadvantages. The pre-shaped cover is more independent of the user operating techniques and does not require a precise matching of its shape with that of the probe. Examples of such covers are those produced by Thermoscan Inc., where the front window (membrane) of the cover does not interact with the probe during the installation. However, such a probe cover maintains the membrane shape quite unpredictably, due to flaccid and pliant optical end of the cover. To assure acceptable performance, the pre-shaped probe covers and the IR thermometer probes have to be produced with tight tolerances which significantly affects their costs.
The second type embraces the probe covers which do not have defined shapes before being placed onto the probe. These probe covers are not sensitive to manufacturer""s tolerances and easily can adapt to the shape of the probe. For example, the probe covers described in U.S. Pat. No. 4,911,559 issued to Meist and Suszinski, have a flat film laminated with backing material. The film stretches around the probe during the installation, thus taking its shape. The other covers, as exemplified by previously mentioned U.S. Pat. Nos. ""862, ""936, ""834, and ""418, while having a pre-shaped body, still require stretch of the membrane by the probe during the installation. The type of the probe covers where the membrane stretches, suffers from significant variations in the IR transmission characteristics due to inconsistency in stretching of the membrane during the installation and even breakage of the membrane because of its small thickness and manufacturer""s tolerances. The non-shaped probe covers occupy less space and generally are more convenient to carry with the IR thermometer. However, this advantage is negated by significantly reduced consistency in the IR transmission.
With respect to attaching the polymer membrane to the body of the probe cover, there are several methods known in the artxe2x80x94all of them require use of some kind of an engagement component to which the membrane is attached one way or another. One method is ultrasonic welding as in the above U.S. Pat. Nos. ""862 and ""418 where the membrane is attached to a supporting ring which is intended for engagement with the IR thermometer probe. Other methods include insert molding, thermal welding, clamping, or laminating with a backing material, as in the above U.S. Pat. No. ""559. The entire probe cover may be fabricated as a unitary device by thermo-forming or injection molding, as described in the above U.S. Pat. No. ""834.
Summarizing a deficiency of the prior art, it may be said that all known probe covers cause inconsistency in detecting infrared radiation due to either poorly controlled shape of the membrane or stretching of the membrane during the installation procedure.
Thus it is an object of the present invention to provide a sanitary barrier between the IR probe and surface of the ear canal.
It is another object of this invention to provide a probe cover which has an optical front that does not change during and after the installation.
Another object of the invention is a probe cover which is less sensitive to the manufacturer""s tolerances.
It is a further object of this invention to provide a probe cover which occupies less space during storage.
It is another object of this invention to provide a probe cover which is less likely to break during the installation.
Still another object of this invention is to provide a probe cover which is easy to install onto the probe and whose optical and thermal properties do not change during the installation process.
The objects of this invention are attained by combining in a probe cover properties of the pre-shaped and non-pre-shaped probe covers. The new probe cover contains two distinct portionsxe2x80x94that which is stable, and the other that may change. This is achieved by a precise pre-shaping only the optical portion of the cover. This part engages with the end of the IR probe and remains unchanged during the installation and temperature measurement, while allowing the rest of the cover to freely change its shape and conform to the probe body configuration for easy installation.